Glomerulosclerosis is a key and common feature of progressive renal failure which is a major cause of morbidity and mortality in the U.S. Although several genetic and environmental insults are known to cause primary glomerulosclerosis, the cellular mechanism(s) by which they initiate the process of glomerulosclerosis is still largely unknown. To elucidate these mechanisms, we generated a novel mouse strain carrying a missense mutation (R394W) in the Wt1 gene which encodes a zinc finger transcription factor and is expressed in the glomerular podocyte. In humans the H/nR394W mutation results in diffuse mesangial sclerosis and early onset renal failure, and Wt1+/R3g4w heterozygous mice mimic this phenotype, developing proteinuria and glomerulosclerosis as early as two months of age. We hypothesize that because Wt1 is a transcription factor, its mutation results in dysregulation of key podocyte-expressed genes which ultimately results in glomerulosclerosis. We will identify these dysregulated genes by comparing the gene expression profile of at-risk mutant kidneys and wildtype kidneys using Affymetrix microarray chips. This work will enable us to identify genes whose altered expression plays a critical, but not yet recognized, role in glomerulosclerosis, thereby expanding the understanding of this disease process. To determine the functional significance of dysregulated gene expression, we will use both in vitro (immortalized podocyte cell lines) and in vivo (ultrasound-mediated gene transfer) approaches to modulate gene expression/pathway function. We will assess the effect of this modulation in terms of cellular phenotype and also the ability to delay disease onset/progression in mutant mice. We have determined that disease onset is dramatically modulated by genetic background on which the Wt1 mutation is carried. We hypothesize that this is due to a modifying gene(s) that differs among mouse strains, and we will localize this locus (loci). The initial cellular changes that initiate the process of glomerulosclerosis and kidney failure in the general population are not well understood. The H/T7R394W mouse carries a mutation known to cause renal failure in humans;it is an excellent and biologically relevant animal model for studying the pathobiology of glomerulosclerosis. It will enable us to identify genetic and cellular changes that occur at the earliest stages of the disease process. It also provides an excellent system for developing and testing new intervention and therapeutic strategies.